Dinucleating Ligand Platforms Supporting Indium and Zinc Catalysts for Cyclic Ester Polymerization

Area of Science:

• Organometallic Chemistry
• Polymer Science
• Catalysis

Background:

• Development of efficient catalysts for stereoselective polymerization is crucial for producing advanced materials.
• Indium complexes are emerging as promising catalysts in organic synthesis and polymerization.
• Chiral ligands play a key role in controlling stereochemistry during catalytic processes.

Purpose of the Study:

• To synthesize novel alkoxide-bridged indium and zinc complexes supported by a chiral dinucleating ligand.
• To investigate the catalytic activity of these indium complexes in the ring-opening polymerization of lactide.
• To evaluate the influence of ligand structure (chiral vs. achiral) on polymer tacticity.

Main Methods:

• One-pot synthesis of indium and zinc complexes using a chiral bis(diamino)phenolate ligand, sodium ethoxide, and metal salts.
• Synthesis of an achiral indium analogue for comparative studies.
• Ring-opening polymerization of racemic lactide (rac-LA) and meso-lactide (meso-LA) using the synthesized indium catalysts.

Main Results:

• Successful synthesis of the first alkoxide-bridged indium complex with a chiral dinucleating ligand and its zinc analogue.
• Indium complexes, both chiral and achiral, effectively catalyze the ring-opening polymerization of rac-LA.
• Chiral indium complex yields highly heterotactic poly(lactic acid) (PLA) (Pr > 0.85), while the achiral analogue produces atactic PLA from meso-LA.

Conclusions:

• The dinucleating ligand platform is effective for synthesizing novel indium and zinc complexes.
• Indium catalysts supported by chiral dinucleating ligands are highly effective for producing stereoregular PLA.
• Ligand structure significantly influences the stereochemical outcome of lactide polymerization, demonstrating the importance of catalyst design.